The present invention relates to a system for controlling the amount of treatment composition to be introduced into an aqueous medium having a content of fats, oils, and/or grease which is to be reduced. More particularly, the invention relates to a system for controlling the amount of treatment composition, such as coagulant, to be introduced into a waste water, such as a laundry waste water, having a content of fats and/or oils and/or grease which is to be reduced, for example, by separation of such fats, oils and grease from an aqueous phase.
Various aqueous media include or become contaminated with one or more fats and/or oils and/or grease. As used herein, the term "FOG" refers to fats and/or oils and/or grease. The FOG content is often present in aqueous media in non-solid form, for example, in a liquid emulsified form, such as the discontinuous phase in an aqueous emulsion. For example, the water utilized in a conventional laundry operation becomes contaminated with FOG, for example, from the articles which are laundered and/or from the detergents and other additives used in the operation. This laundry waste water often cannot be disposed of directly into a publically owned treatment works because of the relatively high FOG concentration.
One approach to overcoming this problem has been to add a coagulant, for example, a cationic coagulant such as one or more cationic polymers and the like, to the laundry waste water so as to coagulate and separate at least a portion of the FOG from the laundry waste water. These coagulated materials are separated from the remainder of the aqueous material and disposed of, for example, as a sludge in a land fill or other suitable disposal facility. The resulting aqueous phase has a sufficiently reduced FOG concentration to be conveniently disposed of in a publically owned treatment works.
One potential difficulty with such a treatment process is that the FOG level in the waste water varies over time so that the demand for coagulant also varies. In general, as the FOG level in a waste water increases, the amount of coagulant needed to provide an aqueous phase having an acceptably low FOG concentration also increases. Thus, the amount of coagulant used is often set at a relatively high level to insure that the water entering the publically owned treatment works is acceptable. The amount of coagulant used is this type of process is often in excess of that needed to provide the acceptably low FOG content.
Directly analyzing an aqueous medium for FOG is often a tedious and time consuming task which may involve taking a sample of the waste water and performing various separation steps to determine the FOG content of the waste water. The time involved in performing these steps may be such as to render the FOG determination obsolete in that the waste water being treated may have a different level of FOG than that determined via this relatively complex procedure.
Martin U.S. Pat. No. 4,855,061 discloses a system for controlling coagulant dosage to water to remove nonsettleable solids, for example, to produce potable water. The coagulant is controlled using a charge sensing means which has a set point that is adjusted in response to the turbidity of the treated water. This patent does not disclose treating relatively heavily contaminated industrial waste waters which contain non-solid contaminants, such as non-solid FOG. Also, the disclosed system relies on measuring the turbidity of the finally treated water which adds to the cost and complexity of the system.
German Patent 3,344,275 discloses a system for treating waste waters, such as laundry waste waters, which include non-solid contaminants, for example, non-solid FOG. Various parameters of the raw waste water are measured. Downstream of these measurements, treatment chemicals are added to the waste water. Flocculent is added in response to the cloudiness measured; alkali and/or acid is added in response to the pH measured; and reducing agent is added in response to the redox potential measured. This German patent does not disclose parameter measurements made downstream from where the treatment chemicals are introduced. The electric charge value of the raw waste water is not used to control flocculent addition. The turbidity of the raw waste water may not provide an accurate indication of the amount of flocculent needed. For example, the non-solid contaminants may, at this point, be dissolved in the water or be of such small size as to not contribute to turbidity. Thus, effective or insufficient flocculent dosing may occur.